Genesis of the Heneshk IOCG deposit, Iran: magnetite mineral chemistry and sulfur isotope

Abstract

The Heneshk Fe ± Cu deposit, a metamorphosed IOCG (Iron Oxide Copper Gold) is situated in Sanandaj-Sirjan Zone, SW Iran. Mineralization occurs as two stratabound ‘U’ shape ore bodies, hosted by a meta-dolomite member of a metamorphic complex. The ore and gangue minerals comprise magnetite, chalcopyrite, hematite, martite, mushketovite, pyrite, barite, calcite, dolomite, and quartz. The successive mineral assemblage formed in the five paragenetic stages (I to V) during an ongoing deformation regime from the plastic to the brittle deformation regime. The mineralization stages comprise stage I, III, and IV. Stage I–III and IV formed in the plastic and the brittle deformation regime by the metamorphic processes in a shear zone, respectively. The concomitant alteration products of these stages comprise sodic, Fe, K, hydrolytic and silicification. The sodic and Fe alterations occur as a pre-mineralization stage and each mineralization stage is accompanied by K and hydrolytic alterations. A late barite-calcite-quartz assemblage (stage V) overprinted on the previous stages (I to IV). Stage I mineralization formed at a depth of ~10 km and temperature of ~300 °C (a high pressure-low temperature environment). The partitioning and substitution of the Mg, Al, Ti, Ni, Cr, Mn, Si, and Zn elements increased in this relatively higher pressure environment cause of the highest concentrations of the Al, Ti, Ni, Cr, and Zn, in comparison with metamorphic magnetite. The mineral chemistry of the Heneshk magnetite (average elemental concentrations) is in accordance with the metamorphic magnetite and can consider as a pure magnetite with the low elemental concentration. Also, the $${{\rm{\delta }}^{34}}{S_{{H_2}S}}$$ Heneshk mineralized fluid ranges between 39.8 to 40.6‰, indicating the contribution of the paleo-evaporates. The pleo-evaporates leached from the older strata during metamorphism, and their precipitation in the form of the sulfide minerals occurs through the TSR (Thermochemical Sulfate Reduction) mechanism.